I recently watched some fascinating live neurosurgery on Channel 4. The patient was awake throughout most of the process and was capable of answering questions posed by the studio audience and viewers phoning in.
The "speech arrest" phenomenon was particularly interesting to witness. The surgeon was removing a large tumour and wanted to ensure that he was not causing any damage to Broca's Area, an area on the brain particularly concerned with speech. He used and electrode to stimulate the approximate area while the patient counted from 1 to 20. If the electrode intruded into Broca's area the patient would "lose" numbers in the sequence but resume consistent counting when the probe was moved away.
Once Broca's Area had been identified the surgeon was able to work past it and go further down into the brain to remove part of the tumour. Unfortunately the tumour was invasive, with webs spreading out deep into the brain, so could not be removed fully. The patient will undergo chemotherapy to try to mitigate this.